Electric discharge devices



March 125, 1958 Filed June 26, 1947 l l'l l'l ly l E. D. M ARTHUR 2,828,438

ELECTRIC DISCHARGE DEVICES 2 Sheets-Sheet 2 Fig.5.

l'l'l l'l' Inventor: 36 Emmet D. Mc Arthur;

r-hs Attorney.

United States Patent ELECTRIC DISHARGE DEVICES Elmer D. McArtlrur, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application June 26, 1947, Serial No. 757,164

16 Claims. (Cl. 313-250) This invention relates to electrical discharge devices of the type useful in the high frequency electrical systems described and claimed in my Patent No. 2,747,087, dated May 22, 1956, and issued on my application Serial No. 179,874, filed August 16, 1950, which application is a continuation-in-part of my application Serial No. 751,358, filed May 29, 1947, and entitled Electric Discharge Devices and High Frequency Systems Therefor, now abandoned. In the above patent, I have described and claimed high frequency electrical systems useful as oscillators, amplifiers, reactance devices and the like and which employ grid-controlled electron discharge devices as elements for controlling the energy within an associated resonant circuit. It is a general object of the invention claimed in my aforesaid application to provide an improved system characterized by a number of advantages such as more convenient and relatively wide band frequency control, a more convenient ampli tude control and structural simplicity resulting from the fact that the number of resonant circuits heretofore normally required to be associated with the discharge device may be reduced, for example, as by the elimination of the resonant circuit heretofore normally associated with the cathode-grid circuit of the device. it is the general object of the invention herein claimed to provide suitable electron discharge tubes or devices useful in such circuits.

The features of the invention desired to be protected are set forth in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following specification taken in connection with the accompanying drawings in which Fig. 1 represents in cross section an electrical discharge device incorporating the basic principle of the invention, together with a schematic circuit in which the device might find employment; Fig. 2 represents similarly an electrical discharge device including a novel reflecting electrode in accordance with one of the alternative principles of the invention in my aforesaid application; Fig. 3 represents similarly an electrical discharge device of the type shown in Fig. 2 modified structurally for the purpose of permitting convenient insertion within a wave guide as its attendant resonant circuit; Fig. 4 represents in cross section an alternative inventive construction functionally similar to that of Fig. 1, together with a schematic illustrative circuit in which it might find employment; Fig. 5 represents an alternative embodiment of the type of structure shown in Fig. 4 but employing the reflecting electrode principle of the Fig. 2; while the Fig. 6 represents an alternative construction of the construction of Fig. 4 in which provision is made for the attachment of suitable external circuits at either end of the cylindrical construction employed.

As is well known in the art, it is a common practice to employ multi-electrode electron discharge devices such as triodes having an anode, cathode and control grid as oscillators by the expedient of providing a feedback circuit between an anode-grid resonant circuit and a cathodegrid resonant circuit. The function of such a feedback circuit is to derive a small oscillatory signal voltage from the anode-grid circuit and employ it to energize the cathode-grid circuit in order that oscillations may be sustained by the amplifying effect on that signal voltage effected by the control grid of the device in the manner well known in the art. Generally speaking, the objects of the invention claimed in my aforementioned application are accomplished by eliminating the necessity of the cathode-grid resonant circuit and consequently also the necessity of feedback circuits. In accordance with the principles of the invention, this result may be reached with an oscillator employing a multi-electrode discharge device, such as a triode having an anode, a cathode, and a control grid, and using space charge control of current flow in a manner similar to prior art oscillators, by reducing the high frequency impedance between the grid and the cathode to a very low value, preferably as near to zero as possible, whereby the latter two electrodes are maintained at essentially the same high frequency potential during operation. To that end, a large by-pass capacitor may be built into the discharge tube structure between the grid and the cathode. In addition, the interelectrode spacings are chosen to meet specific requirements for electron transit time which requirements will be indicated more fully hereinafter.

With this arrangement it becomes possible to generate oscillations with a circuit consisting of a single resonant circuit, such as a cavity resonator between the anode and either the grid or the cathode. Oscillations may be initiated as soon as a predetermined minimum voltage is exceeded on the anode of the device. Those oscillations will have a frequency primarily determined by the char-- acteristics of the cavity resonator or other equivalent resonant circuit and their frequency and amplitude may be further controlled by a unidirectional bias voltage applied to the control grid. The net result is that an oscillator of considerably simplified construction may be provided which has additionally the advantage that it may be caused to oscillate in a more controllable manner throughout a wider continuous range of frequencies and amplitudes.

In my aforesaid application, I have shown that oscil-' lations may be initiated and sustained in a circuit of the foregoing type if the electron transit angle, i. e., the' phase angle phi 5) between the sinusoidal current and voltage of fundamental frequency in the tuned circuit be approximately equal to an odd multiple number of times or 1r radians, that is, that it follow generallythe angle the expression:

satisfying this latter is that during starting of oscillations, the unidirectional anode voltage E the unidirectional grid bias voltage E and the spacing (S in centimeters.

between the grid and cathode be approximately related by the following expression:

where u is the amplification factor of the tube and lambda (A) is the wave length of oscillations.

As further shown in the aforesaid application, another condition for the starting of oscillations is that the Q of the tuned circuit connected between the anode and the grid or cathode be larger than a value given approximately by the following expression:

QQBNu where S is the grid-cathode spacing in centimeters and S is the grid-anode spacing in centimeters.

Referring now to the Fig. fl, there is shown one practical embodiment of the aforesaid principles in a novel electron discharge device structure and an associated resonant circuit in which the desired oscillation may be sustained by operation in accordance with the principle described in my mentioned application. The device may be of generally cylindrical configuration and may comprise a thermionic cathode 1 preferably coated with the usual emission enhancing materials, a grid 2, and an anode 3. The grid and anode may be supported respectively by .the generally parallel transverse members 4 and 5 which may be positioned in fixed relationship with respect to each other by an insulating cylindrical wall .6 of suitable hermetic sealing material such as glass or ceramics. For the purpose of supporting and spacing the cathode .1 with respect to the other electrodes, there may be provided at the lower \end of the cathode an :annular flange 7 which may be juxtaposed to the corresponding horizontal portion of the member 4 and rigidly supported therefrom in spaced relation by the insulating dielectric spacer 8. The dielectric spacer is formed of any suitable dielectric material in order that it may serve as .the capacitor heretofore mentioned and in order that it will have substantially zero impedance within the predetermined range of operating frequencies of the tube. To this end, 1 have found that any suitable material of size sufiicient to give that capacitor a capacity of approximately 50 to 75 micro-micro-farads will serve the purpose. The grid 2 may be supported between the upper cylindrical end of cathode 1 and the anode 3 by any suitable means such as the generally cylindrical member 9 which may form an extension of the transverse member 4. The anode 3 may be supported as by welding to the upper wall 10 of a generally cup-shaped extension 11 of the transverse member 5.

The cathode 1 may be heated to a temperature of thermionic emission by any suitable means such as the resistive coil 12 having loads 13 and 14 afiixed respectively to the lead-in rods 15 and 16. Any suitable means for extending the lead-in rods to the external portions of the tube may be employed. For example, I have indicated the lead-in rods as extending through hermetic glass seals 17 and 18 in corresponding apertures in transverse metal member 19 which forms an hermetic closure for the generally cylindrical portion .20 extending downward from the transverse member 4. A similar lead-in rod 21 aflixed to the cathode ifiange .7 .may extend through another hermetic glass seal 22 to the external portions. Therespective lead-in rods .15., 16 and 21 may be affixed to external terminals 23, 24'and 25 which are attixed to an insulating base member 26 inserted within the rim of the cylindrical portion 26. On the base member there may be provided a suitable orientation protuberance 27 in the usual manner. For the purpose of evacuating the tube during the manufacturing process, any suitable means may be employed, such as the centrally positioned .tubulation 28 which is compressed for sealing off after evacuation of the tube in the usual manner.

Unless care be exercised in design, it .may be found that the distributed inductive and capacitative properties of the space defined by the portions of the structure between the cathode 1 and grid 2 (e. g., the space defined between member 9 and the cylindrical sleeve of the cathode) may constitute a grid-cathode resonant circuit within the range 'ofznormal operating frequencies of the system. That condition 'will give rise to the possibility that the system :may at certain -frequencies oscillate as a conventional tuned grid-tuned anode oscillator of the prior art type already mentioned and thereby interfere with operation in accordance with the principles of the invention. In order to precludethis possibility, it is desirable that all such grid-cathode interspaces be so shaped 4 that they do not constitute resonant cavities within the desired range of operating frequencies. Thus, they are preferably of minimum possible volume whereby their natural resonant frequencies will be much greater than any frequency within the desired operating range.

As a suitable utilization circuit for the tube thus described, there may be provided, in accordance with the principles of the invention described in my mentioned application, the parallel wire or concentric line resonant circuit comprising the co-axial cylinders 29 and 36 shorted at their outer ends by a slidable tuning short 31 in order that the interspace between the cylinders 29 and 30 may be employed as a variable cavity resonator. The outer cylinder 30 is shown as being connected to the grid 2 by means of the spring fingers 32 which resiliently engage the vertical side wall of the cylindrical portion 20 extending from the transverse member 4. The inner cylinder 29 may be connected to the anode for high he quency currents and voltages by means of the annular flange 33 which, together with a spacing member 34 of dielectric material and the transverse member '5, forms a low impedance path .to high frequency, preferably a zero impedance path. Suitable means for imposing preferably unidirectional energizing potentials to the anode and grid with respect to the cathode are shown as the voltage divider 35 energized by abattery 36 and having the slidable contacts 37, 38 and 39 connected respectively to the grid-cathode and anode. It will be obvious that a negative unidirectional potential E is imposed upon the grid in this manner while a positive unidirectional voltage E is imposed upon the anode in accordance with the Equation 2.

In my aforementioned application, I describe an alternative embodiment of the invention therein claimed employing a novel frequency and amplitude control elcctrode which maybe employed in a manner therein described to effect a certain amount of frequency or amplitude control by reflecting a certain amount of the tube current back to the anode-grid space in phase displaced relationship after it has been permitted to pass through the anode interstices. A novel tube structure and associated circuit for accomplishing this effect are shown in Fig. 2 which is substantially identical with a correspond ing figure in the mentioned application. The arrangement of Fig. 2 is substantially the same as that of Fig. l and like numerals have therefore been used to designate like parts throughout. It differs substantially only in the provision of what may be termed a reflecting control electrode 40 positioned on the opposite side of the anode 3 which in this case may take the form of an open mesh Wire structure for the purpose of permitting the ready passage of the current flow through its interstices into the interspace or reflection space between the anode 3 and the reflecting electrode 40. The function of the reflecting electrode 40 is to reflect in controllable phase relationship a number of the electrons, overshooting the anode 3 into the reflection space and subsequently return them to the anode 3 in phase displacement with respect to the ,portion of the tube current in the interspace or reaction space between the grid 2 and the anode 3. To effect such reflection and control there may be applied to the reflecting electrode a variable potential negative with respect to the anode 3 and in some cases even negative with respect to .the cathode 1. To that end, any suitable means'may be provided such as the contact 41 on the voltage divider 35.

structurally, the only substantial difference between Fig.2 and Fig. 1 lies in the provision of the reflector electrode 40 and of any suitable means for mounting it within the discharge device. For example, it is shown as being mounted upon a lead-in conductor 42 extending through anhermetic seal 43 within a central aperture of a transverse supporting member .44. Supporting member 44 may be'sealed to a cylindrical conducting wall 45 which fits into an annular groove 46 within the member 44 and is hermetically embedded therein by the sealing means 47 of solder or like material. In this embodiment the anode 3is suspended from the wall by means of the conductive cylindrical support 48 and may be energized as before by a suitable connection to the transverse supporting member 5 or wall 45. In this modification, the grid 2 is similarly supported on transverse member 4 by the cylindrical support 9. In order to obviate any possible tendency of the reflector electrode 40 and its adjacent parts to oscillate at the frequencies of the system, it may be desirable to provide between the electrode 40 and the anode 3 a path having low impedance to high frequency currents and voltages Within the frequency range of the system. Such a path may be provided by a dielectric spacer 49 between an outer cylindrical collar 59 of the electrode 443 and the support 48. As with the spacer 8, this may form with the collar 50 and support 48 a capacitor of low and preferably substantially zero impedance. In all other respects, this structure is functionally identical with that shown in Fig. l, as will be apparent to those skilled in the art upon study of the drawing.

Referring now to Fig. 3, the tube structure there shown is functionally identical with that of Fig. 2, and. like parts have been used to designate corresponding parts throughout. The structure, however, has been modified in order to permit its convenient and ready insertion within a wave guide which it is adapted to energize. Such a wave guide is represented by the cross sectional walls 51, forming the cross section of the rectangular or square shaped wave guide, for example. It will be noted that in this case the grid supporting member 4 takes the form of a substantially horizontal, preferably annular, plate having an annular flange 52 around its peripheral edge which engages appropriate spring fingers 53 of the wave guide.

The cathode 1 is supported adjacent the spacer 8 by means of the cylindrical metallic member 54 which has transverse annular flanges 55 and 56, the latter engaging the annular ring 7 and supporting it in juxtaposed relation to the depending flange portion 57 of the transverse member 4 with the spacer intervening to constitute with portion 57 and ring 7 the zero impedance capacitor heretofore mentioned. The cathode 1 may comprise any suitable cylindrical structure welded or otherwise secured to the central portion of the ring 7. The cathode 1 may be energized by the heater coil 12 through the lead-in connections 58 and 59 respectively connected to external terminals 60 and 61 for imposition of suitable heating voltages. To complete the hermetic enclosure of the device, there may be provided the generally cup-shaped member 62 of glass or ceramic or similar dielectric insulating material. This member is sealed hermetically to the transverse member 4 and its outer rim as by scaling to the annular flange 52. A metallic spacing member 63 is provided to support the cylindrical member 54 upon the cup-shaped member 62. The anode 3 is supported similarly by means of the cylindrical member 48 which in turn is positioned from the grid supporting member and supported thereon by means of the insulating, generally cup-shaped, member 64 of glass, ceramic or like material sealed respectively to the transverse member flange portion 57 and the cylindrical member 43. The reflecting electrode 40 may be supported within the member 49 by means of the lead-in rod 65 which is rigidly aflixed and positioned within the member 48 by means of the hermetic seal 66 of glass, ceramic or like material. As with Fig. 2, the collar 50 of the reflecting electrode, together with the dielectric spacer 49 and the adjacent portion of the member 48, forms a low impedance capacitor for connecting the reflector electrode to the anode for high frequency current but forms a blocking path for unidirectional current of the respective biasing and energizing potentials. It will be understood, of course, that the structure there shown may be sealed and evacuated during the manufacturing process by any suitable means such as the exhaust tubulation 28 which is compressed after evacuation in the usual manner. The member 48 will form conductive contact with the upper wall of the wave guide by means of the spring fingers 67 circumferentially surrounding a circular open ing in the latter wall;

In Fig. 4, I have shown an alternative tube construction in which the respective electrode members are formed in a generally cylindrical configuration. It will be noted that the device here. shown comprises a preferably metallic envelope 63 of generally cylindrical form which also serves in part as the anode 69 by means of the annular depression 70,. The inner wall of die depression will serve as the-actual anode surface. Concentrically positioned within this structure, there is provided a cathode 71v and a grid 72, the cathode having a central activated portion 73. coated. with suitable thermionic emission enhancing material.

The cathode 71 may be positioned upon a generally cylindrical member 74 extending through the transverse hermetic seal 75 of glass or ceramics which closes the end wall of the envelope 68. It will be observed that the generally cylindrical portion of the cathode is supported on member 74 by a tapered portion 76 thereof and extends into juxtaposition with the anode 69. The cathode may be heated by any suitable means such as the heater coil 77 having a lead 78 conductively connected to the cathode and a second lead 79 extending to the external terminal 80. Heating current may be supplied by any suitable means, such as the battery 81.

The grid 72 is supported concentrically about the cathode in a similar manner, that is, its generally cylindrical portion, 82 is supported by tapered portion 83 of an externally extending cylindrical member 84. In this case the zero impedance capacitor between the cathode and the grid may take the form of a suitable dielectric material positioned between the respective cylindrical structures. For example, the dielectric spacing members 85 and 86 concentrically surrounding the cathode and filling the interspace between the cathode and the grid may beemployed. Member 85 may also serve to support and position the cylindrical portion 87 of the grid. If desired, suitable cooling means for the anode surfaces may be conveniently employed in this construction such as illustrated by the annular cooling vanes 85. Seal 75 may conveniently be constructed of preformed annular glass or ceramic rings 89 and 96, and cylindrical plug 91 positioned concentrically with the respective cylindrical walls of envelope 68 and members 74 and 84 to which they may be sealed during the assembly operation in the usual manner.

As in the case with Figs. 1 and 2, the external resonant circuit may take the form of a cavity resonator comprising uxtaposed concentric transmission line cylinders 92 and 93 tunable by means of the slidable short 94 and aflixed to the respective grid and anode structures by means of the spring fingers 95 which may be annular in construction. Here, again, a low impedance capacity is interposed between the anode and the outer cylinder 93 and takes the form of the dielectric spacer 96 between the l'lIlg 97 and the wall of the envelope 68 as opposite terminals of the capacitor. for energizing the circuit as before, and in view of its similarity corresponding numerals have here been employed.

Fig. 5 shows a modification of the Fig. 4 arrangement employing a reflector electrode. The structure is similar to that of Fig. 4 and like numerals have been employed to designate like parts throughout. It differs substantially only in the fact that in this case the anode 69 has been made of a generally open mesh construction, and within.

the generally U-shaped cross section of the depression 70 there has been employed an annular reflecting electrode 98 having annular flanges, 99 and 100 at either end. which serve, the. function of the collar 50 in the Fig. 2 arrangement. The dielectric low impedance capacitor between The voltage divider 35 is provided,

the collar 50 and the anode supporting walls 101 takes the form in this case of the annular dielectric spacers 102 and 103. These spacers rigidly affix the position of the reflecting electrode with respect to the anode. Any suitable means for supplying the energizing potential to the electrode 98 may be provided such as the lead-in conductor 1% extending through the hermetic seal 105 in the outer wall of the envelope 68. As in the case of Fig. 2, the reflecting electrode 8 may be energized by being connected to the voltage divider through a sliding contact similar to contact 41 of Fig. 2.

In Fig. 6, I have shown a construction which is an alternative to that of Fig. 4, and inasmuch as it is substantially identical except for the one end thereof, like numbers have been used to designate like parts throughout. The construction here difiers from that of Fig. 4 substantially only in the fact that the right end of the envelope is provided with suitable output circuit means in order that a load circuit may be connected to the respective electrodes. case the grid cylinder is provided with a cylindrical extension 1% which extends through the dielectric seal 107, closing the right-hand end of the envelope. With this construction the cylindrical portions of the envelope and the grid, respectively, may in effect be extended to form suitable transmission lines supplying power to suitable external circuits. Such a circuit is shown as the concentric cylinders ltld and 109, respectively, conductively attached to the grid and the anode-envelope by the spring fingers 119 and 111. The advantage of this construction lies in the fact that the load connections to the device may be mechanically separated from the frequency determining elements of the structure, namely, from the resonator comprising tunable transmission lines at the opposite end. It will be understood, of course, that Fig. 6 may be further modified by the provision of a reflecting electrode as in the case of Fig. 5 wherever such addition is desired.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device comprising an hermetically sealed envelope enclosing a plurality of electrodes including an anode, a cathode and a control grid, 21 first conductive member supporting said anode, a second conductive member supporting said grid, said second conductive member being generally parallel to said first conductive member over a region adjacent to where said grid is connected to said second conductive member, a spacer of insulating material between and positioning said conductive members in insulated spaced relation, a third conductive member generally parallel to said second member supporting said cathode on the opposite side of said grid from said anode, and a dielectric spacer of insulating material positioned between said second and third members and constituting therewith a grid-cathode capacitor of substantially zero high frequency impedance within a pre etermined range of operating frequencies of said device.

2. A device as in claim 1 in which said first conductive member and said spacer of insulating material constitute portions of said envelope, said spacer of insulating material being annular and hermetically sealed between said first and second members.

3. A device as in claim 1 in which said conductive members are substantially planar, said second member being annular and having a central opening aligned with said anode, cathode and grid, said electrodes defining a discharge path through said central opening.

Thus, it will be noted that in this 4. A device as in claim 1 in which said conductive members are substantially cylindrical and coaxial, said second member having an opening in its cylindrical wall aligned from said anode, cathode and grid, said electrodes defining a discharge path through said opening.

5. An electric discharge device comprising an hermetically sealed envelope enclosing a plurality of electrodes including a reflecting electrode, an open mesh anode, a control grid and a cathode positioned in that order along a discharge path between said cathode and said reflecting electrode, a plurality of conductive members generally transverse to said path including a first conductive member supporting said anode, a second conductive member on the opposite side of said anode from said reflecting electrode supporting said grid, said second conductive member being generally parallel to said first conductive member over a region adjacent to where said grid is connected to said second conductive member, and a third conductive member on the opposite side of said grid from said anode supporting said cathode, insulating means affixed to said first member positioning said reflecting electrode in insulated spaced relation to said anode, a spacer of insulating material between and positioning said first and second members in insulated spaced relation, and a dielectric spacer of insulating material positioned between said second and third members and constituting therewith a grid-cathode capacitor of substantially zero impedance within a predetermined range of operating frequencies of said device.

6. A device as in claim 5 in which said spacer of insulating material between said first and second members comprises an annular spacer of insulating material heremetically sealed between and positioning said first and second members in insulated spaced relation and constituting a part of said envelope.

7. A device as in claim 5 including a dielectric spacer of insulating material positioned between said reflecting electrode and said anode and constituting a path of low impedance to high frequency currents and voltages between said refiecting electrode and said anode within said predetermined range.

4 8. A device as in claim 5 in which said conductive members are substantially planar, said first and second members being of generally annular configuration and having therein central openings aligned with said reflecting electrode, anode, cathode and grid, said electrodes defining a discharge path through said openings.

9. A device as in claim 5 in which said conductive members are substantially cylindrical and co-axial, said first and second members having openings in their cylindrical walls aligned with said reflecting electrode, anode, cathode and grid, said electrodes defining a discharge path through said openings.

10. An electric discharge device comprising an hermetically sealed envelope enclosing a plurality of electrodes including a reflecting electrode, an open mesh anode, a control grid and a cathode positioned in that order along a discharge path between said cathode and said reflecting electrode through said grid and anode, a plurality of conductive members generally transverse to said path including a first conductive member supporting said reflecting electrode and constituting a portion of said envelope, a second conductive annular member supporting said anode centrally thereof, a third conductive annular member on the opposite side of said anode from said reflecting electrode supporting said grid centrally thereof, said third conductive member being generally parallel to said second conductive member over a region adjacent to where said grid is connected to said third conductive member and a fourth conductive member on the opposite side of said grid from said anode supporting said cathode, an annular hermetically sealed structure affixed between said first and second members positioning said reflecting electrode in insulated spaced relation to said anode and constituting a portion of said envelope,

an annular spacer of insulating material hermetically sealed between and positioning said second and third members in insulated spaced relation and constituting a part of said envelope, and a dielectric spacer of insulating material positioned between said third and fourth members and constituting therewith a grid-cathode capacitor of substantially zero impedance within a predetermined range of operating frequencies of said device.

11. A device as in claim including a dielectric spacer of insulating material positioned between said reflecting electrode and said anode and constituting a path of low impedance to high frequency currents and voltages between said reflecting electrode and said anode within said predetermined range.

12. An electric discharge device comprising an hermetically sealed envelope enclosing a plurality of generally cylindrical electrodes including a reflecting electrode, an open mesh anode, a control grid and a cathode positioned in that order along a discharge path between said cathode and said reflecting electrode through said grid and anode, a plurality of concentric cylindrical conductive members generally transverse to said path including a first conductive member supporting said anode, a second conductive member on the opposite side of said anode from said reflecting electrode supporting said grid, and a third conductive member on the opposite side of said grid from said anode supporting said cathode, insulating means atfixed to said first member positioning said reflecting electrode in insulated spaced relation to said anode, an annular spacer of insulating material hermetically sealed between and positioning said first and second members in insulated spaced relation, and a dielectric spacer of insulating material positioned between said second and third members and constituting therewith a grid-cathode capacitor of substantially zero impedance within a predetermined range of operating frequencies of said device.

13. A device as in claim 12 in which said first conductive member and said annular spacer constitute portions of said envelope.

14. A device as in claim 12 including a dielectric spacer of insulating material positioned between said reflecting electrode and said anode and constituting a path of low impedance to high frequency currents and voltages between said reflecting electrode and said anode within said predetermined range.

15. An electric discharge device comprising an hermetically sealed envelope enclosing a plurality of electrodes including a reflecting electrode, an open mesh anode, a control grid and a cathode positioned in that order along a discharge path between said cathode and said reflecting electrode, a generally cylindrical hollow conductive member supporting said anode across an end face thereof, a pair of conductive members generally parallel to said end face comprising a first generally annular conductive member on the opposite side of said anode from said reflecting electrode supporting said grid centrally thereof, a second conductive member on the opposite side of said grid from said anode supporting said cathode, means supporting said reflecting electrode within said cylinder in insulated spaced relation with respect thereto, a generally cup-shaped member of insulating material hermetically sealed to said first member and to said cylinder positioning said anode in spaced relation to said grid and forming a portion of said envelope, a dielectric spacer of insulating material positioned between said first and second members and constituting therewith a gridcathode capacitor of substantially zero impedance within a predetermined range of operating frequencies of said device, and a generally cup-shaped member of insulating material hermetically sealed to said first member on the opposite side thereof from said first-mentioned cup-shaped member and forming another portion of said envelope.

16. A device as in claim 15 including a dielectric spacer of insulating material positioned between said reflecting electrode and said anode and constituting a path of low impedance to high frequency currents and voltages between said reflecting electrode and said anode within said predetermined range.

References Cited in the file of this patent UNITED STATES PATENTS 2,400,753 Haeff May 21, 1946 2,404,261 Whinnery July 16, 1946 2,411,046 Liimatainen Nov. 12, 1946 2,425,748 Llewellyn Aug. 19, 1947 2,427,693 Ryder Sept. 23, 1947 2,428,609 Beggs Oct. 7, 1947 2,436,397 Morton Feb. 24, 1948 

